Anaesthetic composition

ABSTRACT

A stable anaesthetic composition is described which is particularly suitable for use in cats and dogs. The composition comprises an aqueous solution of an anaesthetically effective amount of water soluble cyclodextrin or a cyclodextrin derivative complex of alfaxalone and a bugger, excluding phosphate buffer pH 7.0, 0.1 M mixed as defined in the British Pharmacopoeia 1998, such that the pH of the solution is from 6.0-8.0.

TECHNICAL FIELD

This invention relates to anaesthetic compositions for use inwarm-blooded animals including birds and mammals, reptiles, fish andamphibians and in particular to alfaxalone-based compositions in whichthe alfaxalone is water-solubilised through the formation of a complexwith a cyclodextrin or a cyclodextrin derivative.

BACKGROUND ART

3α-hydroxy-5α-pregnane-11,20-dione (alfaxalone) is a known anaestheticfor use in a variety of animals. Owing to the fact that in use,alfaxalone has a wide safety margin, rapid induction, high potency,absence of nausea and rapid progress to ambulation, it has been regardedas a very useful anaesthetic. However, the substance is quite waterinsoluble and therefore must be solubilised for effective parenteraluse. Solubilisation in saline has been achieved commercially usingpolyethoxylated castor oil in combination with a small amount ofalfaxalone acetate (21-acetoxy-3α-hydroxy-5α-pregnane-11,20-dione), asteroid which is half as potent an anaesthetic agent as alfaxalone.Nevertheless, its practical usefulness in mammals has been severelylimited since these alfaxalone-based compositions invoke a histamineresponse in a number of species when administered parenterally.

Because of alfaxalone's efficacy, the present inventors have sought tomeet the problem of providing an alfaxalone-based composition which isboth anaesthetically effective and able to be administered parenterallyto mammals without invoking a histamine response.

It is also evident that for practical reasons it is desirable thatformulations of water soluble cyclodextrin or cyclodextrin derivativecomplexes of alfaxalone are presented as ready-to-use solutions. That isno reconstitution is required prior to use. As used in thisspecification, “complex” is to be understood as referring to the watersoluble moiety formed by the hydrophilic/hydrophobic interaction betweenalfaxalone and cyclodextrin or cyclodextrin derivative.

It may be expected that owing to the common use of phosphate buffer,0.1M mixed pH 7.0 (BP 1998) in parenteral formulations, cyclodextrin orcyclodextrin derivative complexes of alfaxalone should be suitable foruse with this buffer. In fact it has been found by the present inventorsthat in formulating a ready-to-use anaesthetic composition, there is afundamental problem in that formulations of the water solublecyclodextrin or cyclodextrin derivative complexes of alfaxalone with pH7.0 phosphate buffer are unstable. By unstable it is meant that acrystalline material was formed in a representative formulation withinabout 7 days when it was stored at 40° C. The presence of such crystalsprecludes the acceptability in use of such a formulation.

DISCLOSURE OF INVENTION

In seeking to provide a stable ready-to-use formulation of cyclodextrinor cyclodextrin derivative complexes of alfaxalone, the presentinventors have established that the nature of the buffer used isimportant.

Accordingly in a first aspect, the present invention consists in astable anaesthetic composition which comprises an aqueous solution of ananaesthetically effective amount of a water soluble cyclodextrin or acyclodextrin derivative complex of alfaxalone and a buffer, excludingphosphate buffer pH 7.0, 0.1M mixed as defined in the BritishPharmacopoeia 1998, such that the pH of the solution is from 4.5-8.0.

In a second aspect, the present invention further consists in a methodof anaesthetising warm-blooded animals including birds and mammals,reptiles, fish and amphibians comprising administering to said animalsan anaesthetically effective amount of a stable anaesthetic compositionwhich comprises an aqueous solution of an anaesthetically effectiveamount of a water soluble cyclodextrin or a cyclodextrin derivativecomplex of alfaxalone and a buffer such that the pH of the solution isfrom 4.5-8.0.

In a third aspect, the present invention still further consists in asterile ready-to-use dosage of an anaesthetic comprising a package whichincludes an aqueous solution of an anaesthetically effective amount of awater soluble cyclodextrin or a cyclodextrin derivative complex ofalfaxalone and a buffer, excluding phosphate buffer pH 7.0, 0.1M mixedas defined in the British Pharmacopoeia 1998, such that the pH of thesolution is from 4.5-8.0 and optionally one or more antimicrobialagents.

In a fourth aspect, the present invention provides a sterile dosage ofan anaesthetic composition comprising a first package containing in dryform, an anaesthetically effective amount of a water solublecyclodextrin or a cyclodextrin derivative complex of alfaxalone and abuffer, excluding phosphate buffer pH 7.0, 0.1M mixed as defined in theBritish Pharmacopoeia 1998, and a second package of sterile water, thebuffer being selected such that a solution formed by dissolving thecontents of the first package with contents of the second package has apH from 4.5-8.0.

In a fifth aspect, the present invention also provides a sterile dosageof an anaesthetic composition comprising a first package containing indry form, an anaesthetically effective amount of a water solublecyclodextrin or a cyclodextrin derivative complex of alfaxalone, and asecond package containing a sterile aqueous solution of a buffer,excluding phosphate buffer pH 7.0, 0.1M mixed as defined in the BritishPharmacopoeia 1998, the buffer being selected such that a solutionformed by dissolving the contents of the first package with contents ofthe second package has a pH from 4.5-8.0.

In a sixth aspect, the present invention still further provides asterile dosage of an anaesthetic composition comprising a packagecontaining in dry form for reconstitution with sterile water, ananaesthetically effective amount of a water soluble cyclodextrin or acyclodextrin derivative complex of alfaxalone and a buffer, excludingphosphate buffer pH 7.0, 0.1M mixed as defined in the BritishPharmacopoeia 1998, and a second package of sterile water, the bufferbeing selected such that a solution formed by dissolving the contents ofthe package with sterile water has a pH from 4.5-8.0.

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

Complexes of alfaxalone with a cyclodextrin or a cyclodextrin derivativemay be readily formed by adding an appropriate amount of alfaxalone to apreformed aqueous solution of cyclodextrin or cyclodextrin derivative.Formation of the complex occurs spontaneously which may then be isolatedby drying. This process is further described in U.S. Pat. No. 4,727,064.Whilst a variety of cyclodextrins or cyclodextrin derivatives may beused, it is preferred to use 2-hydroxypropyl beta-cyclodextrin as thecomplexing agent.

Alternatively, the drying step may be omitted. In this case, therequisite amounts of the buffer components are added to the solution ofthe alfaxalone complex with water being finally added as required togive the desired concentration of alfaxalone in the solution.

A buffer is used in combination with the alfaxalone complex. This buffermust provide a pH for the composition of from 4.5-8.0, preferably6.0-7.0, most preferably about 6.8.

Whilst a variety of buffer compositions may be used, phosphate-basedbuffers are preferred, excluding phosphate buffer pH 7.0, 0.1M mixed (BP1998). This excluded buffer is formed by dissolving 1.361 g of potassiumdihydrogen orthophosphate in sufficient water to produce 100 mL, the pHbeing adjusted by using a 3.5% w/v solution of disodium hydrogenorthophosphate. Particularly preferred are acid-phosphate buffers, suchas citro-phosphate buffer pH 6.5. This buffer is defined in the BritishPharmacopoeia 1998 as a mixture of 29.0 mL of 0.1M citric acid withsufficient 0.2M anhydrous disodium hydrogen orthophosphate to produce100 mL. The amount of buffer used relative to the alfaxalone complex maybe varied.

In a preferred form, the compositions of the invention are presented insterile form packed in vials ready-to-use. Whilst in a variety ofanimals, the compositions will be administered parenterally, in the caseof fish, the composition may be mixed in the water containing the fish.In this way, the alfaxalone passes across the gills where it is absorbedsystemically to produce the requisite anaesthetic/tranquillising effect.Naturally, the water to which the composition is added will depend onwhether the fish are fresh or salt water species.

Other animals that may be effectively anaesthetised with compositions ofthe invention are mammals including marsupials, sheep, horses, pigs,goats, deer, cattle, dogs and cats. It is particularly useful in dogs asthe compositions do not invoke the histamine response of previouslyknown alfaxalone compositions.

The person skilled in the art will appreciate that various antimicrobialagents known in the art may be included in the compositions of theinvention to provide an appropriate level of preservation. It will alsobe appreciated that the compositions of the invention may be sterilisedfor parenteral use by various methods including autoclaving after beingfilled into vials or by filtration through a 0.22 μm filter into sterilevials.

The amount of alfaxalone included in a composition will be determined bythe nature of the animal to be anaesthetised. For guidance, a level of1-100 mg/mL, preferably 5-25 mg/mL, most preferably 7-15 mg/mL may beappropriate.

Stability on storage of the compositions of the invention is animportant attribute. In general terms, the compositions will have ashelf life of at least 6 months when stored at below 25° C., preferablyat least 6 months when stored below 30° C., most preferably at least 2years when stored below 30° C.

MODES FOR CARRYING OUT THE INVENTION

In order to better understand the nature of this invention, a number ofillustrative examples will now be described.

Preparation of Complex Alfaxalone-Cyclodextrin Powder

1. Add 435 grams of hydroxypropyl-beta cyclodextrin (HPCD) to 1 L ofdistilled water and stir to dissolve.

2. Add with stirring to the solution 30 g of alfaxalone.

3. Add sufficient dissolved HPCD to adjust the content of alfaxalone to120 mg per gram of powder when dried.

4. Dry the solution.

Alfaxalone:HPCD Citro-Phosphate Solution

1. Add 435 g of hydroxypropyl-beta cyclodextrin (HPCD) in 1 L of waterfor injection (BP) and stir to dissolve.

2. Add with stirring to the solution 30 g alfaxalone.

3. Add citric acid to the solution from with stirring on the basis of6.09 g citric acid per L of solution.

4. Add sodium phosphate to the solution with stirring on the basis of20.08 disodium hydrogen orthophosphate anhydrous per L of solution.

5. Add water for injection (BP) to give a final concentration ofalfaxalone of 10 mg/mL.

Determination of Stability

A composition was prepared as described above, filtered through a 0.22μm filter under Class A laminar flow conditions and filled, sealed andcapped into clear sterile clear type I glass 13 mL vials withchlorobutyl rubber and aluminium crimp seals. The vials were autoclavedat 121° C. for 20 min with 2 min drying cycle. The composition packed inthe vials was subjected to stability testing with the results obtainedbeing set out below in Table 1.

TABLE 1 TEST Appearance of the SPECIFICATION solution STORAGE ClearColourless Alfaxalone pH CONDITION TIME Liquid 9.0-11 mg/mL 6.5-7.0 ° C.Initial Complies 9.9 mg/mL 6.6 4 3 weeks Complies 9.9 mg/mL 6.8 4 7weeks Complies 10.2 mg/mL 6.7 4 14 weeks  Complies 10.0 mg/mL 6.7 4 24weeks  Complies 10.09 mg/mL 6.7 4 36 weeks  Complies 9.8 mg/mL 6.7 4 12months Complies 10.0 mg/mL 6.7

Conclusion

The product is stable following storage at 4° C. for a period of atleast 52 weeks with no chemical or physical deterioration evident.

A composition was prepared as described above, filtered through a 0.22μm filter under Class A laminar flow conditions and filled, sealed andcapped into clean sterile clear type I glass 13 mL vials withchlorobutyl rubber and aluminium crimp seals. The composition packed inthe vials was subjected to stability testing with the results obtainedbeing set out below in Table 2.

TABLE 2 TEST Appearance of the SPECIFICATION solution STORAGE TIME ClearColourless Alfaxalone pH CONDITION (Mths) Liquid 9.0-11 mg/mL 6.5-7.0 °C. Initial Complies 10.6 mg/mL 6.70 30 1 Complies 10.8 mg/mL 6.9 40 1Complies 10.6 mg/mL 6.8 50 1 Complies 10.5 mg/mL 6.8 30 2 Complies 10.7mg/mL 6.6 40 2 Complies 10.7 mg/mL 6.6 50 2 Complies 10.5 mg/mL 6.6 30 3Complies 10.4 mg/mL 6.7 40 3 Complies 10.4 mg/mL 6.7 50 3 Complies 10.5mg/mL 6.7 30 6 Complies 10.5 mg/mL 6.6 40 6 Complies 10.5 mg/mL 6.6 50 6Complies 10.2 mg/mL 6.6 30 12 Complies 10.5 mg/mL 6.6 40 12 Complies10.8 mg/mL 6.6 50 12 Complies 10.7 mg/mL 6.6 30 15 Complies 10.8 mg/mL6.6 40 15 Complies 10.6 mg/mL 6.6 50 15 Complies  9.6 mg/mL 6.6

Conclusion

The product is stable for 15 months at 30° C., 40° C. and 50° C. whichindicates that the product would have an expected shelf life of at least30 months if stored at 30° C. or lower.

Clinical Evaluation

A trial was undertaken to evaluate the efficacy of a composition of theinvention in a group of 42 cats. The composition used was a sterilesolution of Alfaxalone:HPCD diluted in citro-phosphate buffer pH 6.5 (BP1998) containing the equivalence of 10 mg/mL alfaxalone.

A summary of the dose range used, route of administration, mean recoverytime to head lift and sternal recumbency after anaesthesia and meansurgery time is presented in Table 3.

The mean dose of alfaxalone, where alfaxalone was used as the soleanaesthetic, was 4.5 mg/kg for induction and a mean total dose of 5.8mg/kg bodyweight. The mean recovery time was 30 minutes to head lift and44 minutes to sternal recumbency. The mean procedure time was 9 minutes.

Cats ranged in age from 2 months to 16 years of age.

TABLE 3 Use of Alfaxalone: HPCD sterile Injection in cats Dose Mean TimeTotal Dose Suppl. (mg/kg) (min) Number of Range mg/kg Dose Route InduceTotal Head Lift Sternal Surgery Observations   0-4.9 no I/v 3.8 3.8 2127 5 13   0-4.9 yes I/v and I/v 2.3 3.7 38 48 11 3   0-4.9 gas I/v andgas 3.4 3.4 35 43 34 7 5.0-7.5 no I/v 4.6 5.8 16 30 6 3 5.0-7.5 yes I/vand I/v 3.3 6.4 35 60 19 6 5.0-7.5 gas I/v and gas 7.2 7.2 13 20 23 47.6-10.0 no I/v 8.3 8.3 45 60 5 1 7.6-10.0 no I/m 8.6 8.6 60 85 5 17.6-10.0 gas I/m and gas 10.0 10.0 ns ns ns 1 7.6-10.0 yes I/m and I/v7.5 10.0 95 110  5 1 >10.0 yes I/v and I/v 10.0 16.7 35 80 14 2 Summary4.5 5.8 30 44 9 Alfaxalone Only Doses *ns = not specified

Procedures performed under anaesthesia included:

Abscess 3 cases Amputation 1 case Castration 20 cases Castration/3^(rd)eyelid flap 1 case Spey 8 cases Spey/pyometra 1 case Eye ablation 1 caseRemoval of cast 1 case Dental procedures 2 cases Lung biopsy 1 caseTumour removal 1 case Suture wounds 2 cases

Four of the 42 cats were reported to be “jumpy on recovery”, one catvomited on recovery and one cat had a prolonged time to head lift butwas then on its feet shortly after lifting its head.

These results clearly indicate that the compositions of the inventionare clinically efficacious.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

The invention claimed is:
 1. An anaesthetic composition, comprising: anaqueous solution of an anaesthetically effective amount of a watersoluble cyclodextrin or a cyclodextrin derivative complex of alfaxaloneand buffer effective to stabilise the alfaxalone and provide a pH in thecomposition of about 6.8, wherein crystalline material does not form inthe composition within about 7 days when stored at 40° C., and the watersoluble cyclodextrin or cyclodextrin derivative is 2-hydroxypropylbeta-cyclodextrin, and the alfaxalone in a concentration of 7-15 mg/mL.2. A sterile ready-to-use dosage of an anaesthetic comprising a packagewhich includes an anaesthetic composition as claimed in claim
 1. 3. Amethod of anaesthetising warm-blooded animals comprising administeringto said animals an anaesthetically effective amount of a composition asclaimed in claim
 1. 4. A method of anaesthetising warm-blooded animalscomprising administering to said animals an anaesthetically effectiveamount of the dosage of claim
 2. 5. The anaesthetic composition of claim1, wherein the composition has a shelf life of at least 2 years whenstored below 30° C.
 6. A method of producing a packaged sterileanaesthetic composition, comprising: forming an aqueous solution of a2-hydroxypropyl beta cyclodextrin complex with alfaxalone and a buffer;introducing the solution into a container; sterilizing the solution andthe container by autoclaving; wherein, the solution has a pH of about6.8; the concentration of alfaxalone is 7-15 mg/mL; the composition hasa shelf life of at least 6 months when stored below 30° C.; andcrystalline material does not form in the composition within about 7days when stored at 40° C.
 7. The method of claim 6, wherein thecomposition has a shelf life of at least 2 years when stored below 30°C.